The present invention relates to a vibration suppression device of a power train including an engine mounted on a vehicle body and belongs to a technical field of a vibration suppression of a motor vehicle.
A four-wheel drive vehicle is normally equipped with a transfer device to transfer engine power derived from an engine to front and rear wheels respectively. The transfer device of the four-wheel drive vehicle whose engine is disposed in a vehicle width direction generally comprises an input shaft extending in the vehicle width direction and inputting the engine power from a front engine via a transmission, an output shaft extending backward of the vehicle with crossing the input shaft at a right angle, a bevel gear provided between the input and output shafts, and a case storing these shafts and bevel gear and including a journal to support the above-described output shaft.
In such a structure where the transfer device as a mass is located behind the engine, vibration is generated around an engine axis of the engine resiliently mounted on the vehicle body, and it induces vibration of the transfer device in a vertical direction. As a result, there may occur a problem that such vibration transfers to the vehicle body and causes unpleasant noise in a vehicle compartment.
One of methods to solve this problem is disclosed in, for example, Japanese Patent Laid-Open Publication No. 10-291423 (see page 6, FIG. 5). Namely, the method is that there is provided a dynamic damper at an extension housing which is attached to the transfer device and extends backward of the vehicle and this dynamic damper suppresses vibration of the transfer device and/or a power train.
Herein, the dynamic damper is normally configured of a resilient member and a mass member, and it is attached to the transfer device such that the mass member is mounted on it via the resilient member. Further, the resilient member is located under a in a position where the temperature changes greatly, for example, near an exhaust manifold or an exhaust gas purification device. Accordingly, the resilient members are exposed to severe temperature-changes, and thus a resilience of the resilient member also changes according to the temperature change. As a result, the resonance frequency of the dynamic damper changes to a high frequency when it becomes hard under a relatively low temperature circumstance, while it changes to a low frequency when it becomes soft under a relatively high temperature circumstance. However, the dynamic dumper is originally designed so as to provide its substantially constant resonance frequency which is equivalent to a peak frequency of the vibration of the power train when the power train generates its greatest vibration to be suppressed. Accordingly, if the resilience of the resilient member changes, the resonance frequency of the dynamic damper also changes from the above-described peak frequency. As a result, there is a problem that the vibration of the transfer and/or the power train may not be suppressed properly.
Further, in the case where there is newly provided the dynamic damper described in the above patent publication, there are such other problems that a trial of weight reduction of the vehicle body may he disadvantaged by adding an additional weight of the dynamic damper newly provided, and an additional space may be required in order that the dynamic damper is disposed in a narrow space.